The present invention relates generally to analog flueric devices and more specifically to a flueric device which is capable of being used as a density concentration, acceleration and attitude sensor.
There are numerous ways to sense the concentration of one fluid in another, fluidically. These methods are categorized by the acutal physical property that they utilize for inferring the concentration. There are essentially three properties that fluidics exploits to sense the difference between an unknown gas/fluid and a reference: (1) viscosity, (2) ratio of specific heats, and (3) density.
Patents covering the use of these three properties or combination thereof abound. Viscosity is used by Drzewiecki and Manion in U.S. Pat. No. 3,952,576. When a change in fluid viscosity is affected in one control channel of a fluidic proportional amplifier and not in the other, the jet in the amplifier is caused to deflect due to a difference in flows hence a signal output is realized as a function of difference in viscosity which can be directly related to the concentration of a known gas/fluid in another.
Viscosity and density are used in combination in the orifice-capillary bridge concentration sensor as shown in U.S. Pat. No. 3,771,348 to Villarroel. Changes in both density and viscosity produce changes in resistance. The orifice resistance is a function of density, and the capillary resistance is a function of viscosity. The pressure between the orifice and capillary changes according to these parameters and when compared with a reference orifice/capillary pair produces a differential pressure that is a function of concentration.
The ratio of specific heats determines the speed of sound through a medium. Cavity oscillators, edge tone oscillators and feedback oscillators, all have frequencies that are dependent on the speed of sound. As changes of concentration occur, the frequency of operation changes, and this change can be directly relative to the concentration. An example of using an oscillator to determine concentration is illustrated in U.S. Pat. No. 3,756,068 to Villarroel and Joyce.
Lastly, but certainly not inclusively, density or relative weight in a force/acceleration field is used in vortex concentration sensors illustrated in U.S. Pat. No. 3,765,224 to Ostdiek and Manion. The vortex device utilizes a radial flow field where a reference gas and an unknown gas are admitted on the two semicircular sides of a radial flow, the line of separation being vertical or inline with the gravitational field. When a denser (heavier) fluid is introduced on one side, a weak vortex is formed since the heavy gas at the top falls on the lighter and the lighter fluid rises through the heavy one. This weak vortex can be detected by angle of attack sensors and is capable of sensing concentrations, say of CO.sub.2 in N.sub.2, of less than 1 ppm. The main problem with this device is it has an extremely high output impedance. As with the vortex rate sensor, the sensitivity is greatly degraded (by the ratio of input-to-output impedance) when loaded into a fluidic system. This degradation is often of the order of 100 and more. Thus, there exists a need for an improved density type flueric concentration sensor with low output impedance.
Flueric laminar jet linear accelerometers are well known. A flueric laminar jet accelerometer is illustrated in U.S. Pat. No. 3,971,257 to Drzewiecki. A laminar jet stream is emitted from a nozzle into a chamber vented to an ambient environment. A pair of fluidic output sensors are disposed downstream of the vented chamber symmetrically about the center axis of the laminar jet stream to monitor deflection of the jet stream in an applied force field and provide a differential output as an indication of the deflection and applied force field. Although being an improvement over prior laminar jet accelerometers, the flueric laminar jet linear accelerometer of U.S. Pat. No. 3,971,257 is a very insensitive device and requires acceleration fields of a thousand times gravity to obtain a sensed reading. In spite of this limitation, the flueric accelerometer has a very low output impedance that is readily interfaced with other fluidic devices and circuits. Thus, there exists a need for a flueric laminar jet linear accelerometer which maintains its low output impedance with the greater sensitivity.